1. Field of the Invention
This invention relates generally to interconnection systems and, in particular, to interconnection systems for solid-state devices.
2. Description of the Related Art
Microelectromechanical systems (MEMS) often include integrated electrical and mechanical components that require, respectively, electrical interconnections and mechanical couplings. MEMS fabrication techniques, such as deep reactive ion etching (DRIE) can produce complex three dimensional structures with components that are difficult to interconnect. MEMS devices may include regions that are completely etched through from a top surface to a bottom surface of a semiconductor wafer, such that a conventional via-connected, multi-planar interconnect system within a device substrate is not feasible.
For example, a conventional, full-bridge accelerometer with cantilevered seismic masses and strain gauges can be fabricated as a MEMS structure, but the electrical connection of the bridge requires complicated crossover structures or very delicate wire-bonding on a device that may be on the order of 1 millimeter across. The interconnection problem may be exacerbated when multiple devices are fabricated on a single MEMS substrate, such as a tri-axial accelerometer, for example, where several crossover structures may be required and multiple wire bonds must be made to the MEMS device and to contacts that provide external access to the MEMS device, such as a lead frame. Additionally, wire bonds may reduce the reliability of a MEMS device in harsh temperature, shock and vibration environments such as automotive and military applications.
A Wheatstone bridge on the surface of a MEMS device is connected by through-wafer-vias to terminals on the outside surface of a wafer bonded to the MEMS wafer. As an alternative to wafer vias, leads are brought out horizontally. This requires an insulating bond on the outside.
Accordingly, there is a need for a MEMS packaging that provides interconnections without on-device crossovers and bond wires. There is a further need for MEMS packaging that connects two or more points on a MEMS wafer with conductive paths on the inside of an opposing second wafer.